Tissue damage can be caused by a substantive loss of tissue due to ischemic, traumatic, toxic, or inflammatory injuries in which cells within the tissue are destroyed by apoptosis or necrosis. Tissue damage can occur in a number of acute and chronic diseases and conditions. The degree to which tissue damage occurs is mediated by many factors, including the type of disease or injury, the level of or severity of inflammation or trauma associated with the disease or injury, the location of the tissue damage, and the vascular sufficiency of the tissue.
Recent evidence suggests that erythropoietin (EPO), a member of the Type-1 cytokine family, commonly associated with the maintenance of hematocrit may also play an important role in attenuating tissue damage through the interaction with its receptor, EPOR (Brines et al., 2004, Proc. Natl. Acad. Sci. USA, 101(41):14907-12). Although it is hypothesized that EPO may provide compensatory responses that serve to improve hypoxic cellular environment and modulate programmed cell death caused by metabolic stress, the underlying molecular mechanism is yet to be clearly understood.
Based upon this observation, investigators have explored the use of EPO in various indications. As an example, investigators have explored the use of EPO as a potential treatment for cancers based upon the observation that EPO used to treat anemia in oncology patients not only rectified the anemia but resulted in an enhancement of the well-being of the oncology patient as well. (see U.S. Pat. No. 6,579,525 and Blau C. A., 2007, Stem Cells 25(8):2094-7). U.S. Pat. No. 6,579,525 to Haran-Ghera et al. relates to the use of recombinant EPO for the treatment of multiple myelomas and hypothesizes that EPO induces an immune response to the tumor. Additionally, U.S. patent application Ser. No. 11/093,177, publication no. US 2005/0267027, discloses the use of EPO to inhibit angiogenesis in tumors by reducing HIF-1α and/or VEGF expression in the tumors.
However, EPO as a potential tissue protective agent suffers from serious disadvantages due to its erythropoietic effect. In particular with chronic dosing, such as would be envisioned in indications such as cancer and inflammation, the frequent applications of therapeutic doses of EPO may significantly increase a subject's hematocrit, which may lead to hypertension, seizures, and vascular thrombosis.
Further, with regard to cancer, the potential of EPO as a therapeutic has not been realized. It has been determined that several types of cancer, such as breast cancers, express, and tend to over-express, erythropoietin receptors. This has led to concerns that the therapeutic use of EPO to treat cancer would lead to further growth of the tumor as opposed to a regression of the tumor's development (see Blau, 2007, supra, and U.S. patent application Ser. No. 10/432,899, published as US 2005/0260580). This concern has been borne out in the clinic as several trials of EPO within various cancer indications have been halted due to an increase in mortality due to tumor growth (Blau). In light of these adverse clinical outcomes the FDA has attached a Black Box warning on approved EPO products cautioning against their use in unapproved cancer indications.
Additionally, mature human EPO protein is a 165 amino acid protein having a molecular weight of about 30.4 kDa measured by mass spectroscopy. The recombinant protein can be produced in Chinese hamster ovary cells in an expensive and labor intensive process that is highly regulated. Further, EPO must be stored under stringent conditions to maintain its activity. Given these limitations EPO is not an ideal candidate to address public emergencies, such as the release of a toxic agent such as radiation or a chemical agent, either through an industrial accident or act of terrorism or war that would require the rapid mass production of the therapeutic for wide distribution.
Accordingly, there is a need for tissue protective treatments that have little or no potentially detrimental effects and can be made readily available to the public.